FIELD OF THE INVENTION
The invention relates to a semiconductor circuit, in particular for use in an integrated module. The semiconductor circuit has at least one operational assembly with a drive circuit, such as a microprocessor, and with a data memory. The semiconductor circuit also has at least one initialization assembly for testing and/or for initializing the operational assembly and the operational assembly is connected to the initialization assembly via at least one disconnectable connecting line.
In the above-mentioned semiconductor circuit of the generic type, the data memory is frequently constructed as a non-volatile, programmable data memory. When a semiconductor circuit is being completed, data are written to the data memory, for example with the aid of the initialization assembly. Furthermore, it is possible to place the operational assembly, with the aid of the initialization assembly, in a state in which the operational assembly can be tested. For this purpose, the initialization assembly is connected to the operational assembly via connecting lines. Such connecting lines are made of conductive material, such as a conductive polymer, in particular polysilicon, or metal.
In order to increase the reliability of systems for which the semiconductor circuits of the generic type are used, after the semiconductor circuit has been completed the initialization assembly is permanently disconnected from the operational assembly. As a result, specifically the functions of the initialization assembly are reliably deactivated, so that changes that are undesired in this regard are impossible. For this purpose, after the semiconductor circuit of the generic type has been completed the above-mentioned connecting lines are disconnected. This is done, for example, by electrical firing, by laser cutting or else by mechanical disconnection. In particular in the case in which the connecting lines are interrupted by laser cutting or by mechanical disconnection, the semiconductor circuit is subsequently embedded in an insulating housing material which additionally ensures protection against undesired changes.
In order to make it more difficult to reactivate the disconnected connecting lines for purposes of tampering, it is known in the prior art to dispose the connecting line in the deepest possible layer of the semiconductor circuit. It is then possible to reconnect the free ends of the disconnected connecting line to one another only in a particularly costly and complicated fashion. For this purpose, the connecting line would initially have to be exposed. This is particularly difficult since the layers of the semiconductor circuit that are located above the connecting line have to be removed without destroying the semiconductor circuit. It would then be possible subsequently to make a conductive connection of the free ends of the connecting line. In practice, this does not usually take place, since the semiconductor circuits of the generic type are well protected against undesired changes by the measures described above.
Despite the favorable construction of the semiconductor circuits of the generic type in terms of an undesired reactivation of the initialization assembly, changes to the semiconductor circuit may nevertheless occur.
Published, European Patent Application EP 0 172 108 A1 discloses a semiconductor circuit in an integrated module which has a disconnectable connecting line that is protected between a circuit and a cover plate which is connected to ground. The connecting line can only be reached by a testing probe, if the testing probe penetrates the cover plate, which causes a short circuit in the testing probe. Therefore one can not read a signal of the connecting line with the testing probe. After removing the cover plate the disconnected connection can be reconnected.
U.S. Pat. No. 5,473,112 discloses an integrated semiconductor circuit that regulates access to a non-volatile memory with a logic circuit or via input/output pins with a multiplexer. An initialization line of the multiplexer is protected by screening lines that have a defined potential range. An examination of the semiconductor chip via electronic ray scanning or ion milling causes a short circuit of the initialization line with the screening line, therefore making access to the memory via the input/output line impossible.